1. Technical Field
The present disclosure relates to an image sensor and a fabrication method thereof, and more particularly to an image sensor having reduced crosstalk between pixels, and a fabrication method thereof.
2. Description of the Prior Art
An image sensor is a device that may convert optical images into electrical signals. The demand for devices with image sensors having improved performance such as, for example, digital cameras, camcorders, PCSs (Personal Communication Systems), gang machines, security cameras, micro-cameras for medical applications, and robots has increased.
A metal oxide semiconductor (MOS) image sensor is driven in a simple and relatively easy manner and can be embodied using various scanning methods. Also, MOS processing technology allows for the miniaturization of products and also reduces production costs because signal processing circuits can be integrated onto a single chip. Moreover, MOS image sensors have very low power consumption, and thus can be applied to products having limited battery capacity. Furthermore, with MOS image sensors high resolution may be achieved for products used in conjunction therewith. Accordingly, the demand for the MOS image sensor is increasing.
The pixel of the MOS image sensor photoelectrically converts incident light to accumulate charges corresponding to the amount of the light in a photodiode, and then reproduces image signals in a read-out operation. However, the charges produced by incident light may not accumulate in the photodiode of the corresponding pixel, but may instead move to and accumulate in the photodiode of an adjacent pixel, causing crosstalk between pixels.
As shown in FIG. 1, crosstalk between pixels can be divided into two categories: optical crosstalk A and electrical crosstalk B. For example, optical crosstalk A refers to when light incident through a microlens and/or a color filter is not transferred to a desired pixel, but is instead transferred to the photodiode of an adjacent pixel due to refracted light resulting from refraction from the following surfaces: (a) the surface of a multilayer structure consisting of interlayer insulating films 3, 4 and 5 having different refractive indexes, (b) the surface of non-uniform films, or (c) reflected light 6 resulting from reflection from the upper or side surface of metal interconnections M1, M2 and M3. Next, electrical crosstalk B refers, for example, to when charges produced in the bottom or side of a photodiode are transferred to the photodiode 2 of the adjacent pixel due to long-wavelength incident light 7.
When crosstalk occurs, in the case of black and white image sensors, the distortion of images can occur due to a reduction in resolution. Also, in the case of color image sensors including a color filter array (CFA) having red, green and blue filters, the possibility of crosstalk due to incident long-wavelength red light is higher, thereby possibly resulting in poor tint. In addition, a blooming phenomenon, in which adjacent pixels in a picture become hazy, may also occur.
Thus, there is a need for an improved image sensor which provides reduced crosstalk between pixels and for a method of fabricating the same.